1. Field of the Invention
The present invention relates to a solid state image sensing device and specifically relates to a solid state image sensing device possessing a gamma correction means for correcting discrepancies in the gamma characteristics of individual pixels pertaining thereto.
2. Description of the Related Art
Among heretofore used solid state image sensing devices, there are no instances in which the gamma characteristics of individual pixels differ and therefore no such devices that carry out gamma correction for individual pixels. If, however, the use of a photoelectric conversion film engendered a situation in which the gamma characteristics of individual pixels differed, then gamma characteristics would have to be corrected for each pixel, and each pixel would require a different non-linear conversion to carry out such correction in a solid state image sensing device wherein an output corresponding to a quantity of incident light is converted to linear form.
However, carrying out a non-linear conversion is impractical inasmuch as it generally involves a method employing a look-up table, which constitutes an enormous quantity of data for the gamma correction alone, and processing is extremely complex and cumbersome.
A first object of the present invention is to provide a solid state image sensing device capable of easy correction of different gamma characteristics in individual pixels.
In order to achieve the aforementioned object, the solid state image sensing device is furnished with a plurality of elements which receive a light signal and output an electrical signal corresponding to the amount of light received, and said solid state image sensing device comprises:
a plurality of photoelectric conversion elements having individual gamma characteristics for each elements;
a logarithmic conversion unit which performs a logarithmic conversion of, respectively, an electrical signal generated in the photoelectric conversion element and the output from each photoelectric conversion element; and
a gamma correction circuit which corrects discrepancies in the gamma characteristics of the output from each photoelectric conversion element, said output having undergone the logarithmic conversion by the logarithmic conversion unit.
Due to the aforementioned construction, a logarithmic conversion unit provides a logarithmic conversion for each pixel in an electrical signal output by a photoelectric conversion element, and said electrical signal attains a linearity corresponding to the logarithm of a light signal. Furthermore, the slope of this linearity depends on the gamma characteristics of the photoelectric conversion element, and therefore the gamma characteristics of the photoelectric conversion element can be corrected by correcting the linear slope, that is, through multiplication and division operations alone.
These and other objects, advantages, and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.